Outside the tiny public library, a dozen striking grape pickers wait for a meeting called by their employer. "He wants to force us back to work,'' says one woman. "We are hungry but we will wait for a better wage,'' says another employee of Keurboschkloof farm.

After trouble in South African labour relations last year led to a two-month violent standoff in the mining sector, the country's economy is now under pressure from a stop-start farm labourers' strike in the £850m-a-year fruit and wine sector. Since November, low-skilled workers demanding a pay increase to 150 rand a day (£10.65) have clashed with police and been arrested in their hundreds. Amid allegations of excessive police force, three have died.

Unions and charities supporting the Western Cape's 500,000 farm workers say pay and working conditions are so bad that South African wines, table grapes and granny smith apples should be as unacceptable to responsible British consumers as they were under apartheid. "The government should be forcing the farmers to the table but it is not,'' said Nosey Pieterse, secretary general of the black agricultural sector union, Bawusa. "Our only weapon left is for the foreign buyers to pledge that unless the conditions are addressed, they will no longer import South African products.''

Whereas striking miners are typically up against faceless London-listed corporations, farm workers face a different battle. Most are not unionised, and many are illiterate and face the danger of eviction because they live on their employers' properties. Poorly enforced labour rights and tenancy legislation, as well as the pitifully low statutory daily minimum wage in the sector – 69.39 rand (£4.92) – perpetuate paternalism.

When farmer Anton De Vries arrives, slightly late, at De Doorns library, he hugs each of the female strikers. They laugh and, if anything, seem pleased to see him. "You see, there is no problem,'' says De Vries, whose company, South African Fruit Exporters, manages Keurboschkloof farm and its 300 employees. "They want to work. They are being intimidated into striking. We do lots of empowerment things in our company.''

At the meeting, De Vries offers a range of pay rises to get workers back under vines which, all around the Hex valley, are drooping with ripe table grapes. "He offered increases of 10-12 rand (71-85p) per employee,'' said Sandile Keni, provincial organiser for the Food and Allied Workers' Union, who was in the meeting. "Those earning 90 rand [a day] were offered 100 rand, those on 127 rand would go up to 137 rand (£9.72). The workers are considering the offer.''

De Vries is the second employer in a week to offer a settlement – a move welcomed by unions, though they would prefer a centralised form of negotiation. But with only 3%-6% of the workforce in a union, the employers have the upper hand. Many appear, with the tacit blessing of the government, to be waiting for the outcome next month of annual talks expected to lead to a modest increase in the statutory minimum wage.

But those fighting for farm workers' rights say much more needs to be done. A 2011 report by Human Rights Watch found widespread exposure to pesticides, lack of access to drinking water or sanitation, and a failure to pay sick leave. While the system of payment in alcohol has largely been abolished, the Western Cape still has the highest rates in the world of foetal alcohol syndrome.

Pieterse said the farm owners, not workers, had benefited from the ending of apartheid. "In the first 10 years of democracy, the wine industry grew tenfold, from 20m litres' output before 1994 to 220m litres. The farm workers' conditions went the other way. Tenure rights laws were not accepted by the farmers. More than 1 million farm workers were evicted. They remain slaves on the land of their birth.''

He denied unions had intimidated workers into prolonging the strike, saying they were facing huge pressure to return to work while fearing punitive dismissals if and when they did.

Of Western Cape's fruit production, 58% is exported. In Britain one of the main importers is Tesco. Its director of ethical trading, Giles Bolton, said Tesco put an "ethical buying hub'' into South Africa three years ago to keep tabs on suppliers' treatment of staff.

He said: "The whole South African agriculture sector is very little unionised and it would help if there was a more mature industrial relations atmosphere. However, it is not for us as a company to dictate to a foreign country that 'you must pay X'. I think the African National Congress government would query us for saying such a thing.''